The present invention relates generally to thermally enhanced oil recovery. More specifically, this invention provides a method and apparatus for improving the uniformity of steam quality equalization during multiple well injection from a common header. In the recovery of oil from reservoirs, the use of primary production techniques (i.e., the use of only initial formation energy to recover the crude oil) followed by the secondary technique of water flooding, recovers only a portion of the original present in the formation.
Moreover, the use of certain enhanced oil recovery (EOR) techniques is also known in the art. These techniques can generally be classified as either a thermally based recovery techniques, i.e., utilizing steam, or a gas drive method that can be operated in a miscible or non-miscible manner.
Methods which employ steam are effective in the enhanced recovery of oil because the steam heats the formation, lowers the viscosity of the oil, and thus, enhances the flow of oil towards a production well. Moreover, these methods have become preferred methods for enhanced recovery of low gravity, high viscosity oils because steam can cost effectively provide heat to such oils.
Ideally, the petroleum reservoir would be completely homogenous and the steam would enter all portions of the reservoir evenly. However, it is often found that this does not occur. Instead, steam selectively enters a small portion of the reservoir. Eventually, "steam breakthrough" occurs and most of the steam flows directly from an injection well to a production well, bypassing a large part of the petroleum reservoir.
It is possible to overcome this problem with various remedial measures, e.g., by plugging off certain portions of the injection well. For example, see U.S. Pat. Nos. 4,470,462 and 4,501,329, which are hereby incorporated by reference for all purposes. However, to institute these remedial measures, it is necessary to determine which portions of the reservoir are selectively receiving the injected steam. This is often a difficult problem.
Various methods have been proposed for determining how injected steam is being distributed in the wellbore. Bookout ("Injection Profiles During Steam Injection", SPE Paper No. 801-43C, May 3, 1967) summarizes some of the known methods for determining steam injection profiles and is incorporated herein by reference for all purposes.
The first and most widely used of these methods is known as a "spinner survey." A tool containing a freely rotating impeller is placed in the wellbore. As steam passes the impeller, it rotates at a rate which depends on the velocity of the steam. The rotation of the impeller is translated into a an electrical signal which is transmitted up the logging cable to the surface where it is recorded on a strip chart or other recording device.
As is well known to those skilled in the art, these spinners are greatly effected by the quality of the steam injected into the well, leading to the unreliable results or results which cannot be interpreted in any effective way.